open_then_run: Hold fd with OwnedFd instead of File/Dir

Stop using Dir from the nix crate. As we're now holding the FD by
OwnedFd, Dir doesn't allow us to transfer out the FD ownership.

Test: TH
Bug: 243500154
Change-Id: Ic5f2ead12f71c4cd2d8b34be8bd9dd548f49a87b
diff --git a/authfs/tests/Android.bp b/authfs/tests/Android.bp
index ebc6dd4..990daf3 100644
--- a/authfs/tests/Android.bp
+++ b/authfs/tests/Android.bp
@@ -33,8 +33,8 @@
         "libanyhow",
         "libclap",
         "libcommand_fds",
+        "liblibc",
         "liblog_rust",
-        "libnix",
     ],
     test_suites: ["general-tests"],
     test_harness: false,